Blood Physiology
Hematopoiesis
• Blood cell formation
• Occurs in red marrow
– Flat bones
– Skull
– Pelvis
– Ribs
– Sternum
• Lymphocytes that form T cells and B cells are
also formed in lymph nodes
Hematopoiesis
• In bone marrow, all blood cells originate from a
single type of stem cell.
• Stem cell divides it becomes either
– An immature red blood cell
– A white blood cell
– A platelet-producing cell
• The immature cell then divides, matures
further, and ultimately becomes a mature red
blood cell, white blood cell, or platelet.
Hematopoiesis
Red Blood Cell Formation
• Reticulocyte
– Young RBC, still contains ER
– Matures within 2 days of release in circulation
• Erythropoietin
– Controls the rate of erythropoiesis
– Hormone released by kidneys
Red Blood Cell Formation
• Mature red cells cannot divide to reproduce
– No nucleus
– No organelles
• Life span ~120 days
– Old/damaged cells removed by spleen and liver
– Hemoglobin is recycled
WBC & Platelet formation
• Both hormone controlled
– WBC’s – Interleukins & colony stimulating factors
– Platelets – thrombopoietin
• Hemostasis
– “Stoppage of bleeding”
– Stimulated by damage to blood vessels
– 3 events, rapid sequence
Hemostasis
1. Vascular Spasms
– Vasoconstriction
•
•
Narrow blood vessel
Limit blood loss
2. Platelet Plug Formation
– Platelets “stick” to damaged tissue
– Attract more platelets to area
– Also called “white thrombus”
3. Coagulation
Coagulation
1. TF is released by injured tissue
– Stimulates clotting
2. PF3
– Coats platelets
– Interacts with TF, vitamin K, clotting factors, Ca
– Activates the “clotting cascade”
3. Prothrombin is converted to thrombin
4. Thrombin mixes with fibrinogen to form
fibrin
– Forms the “clot”
Coagulation
• Entire sequence of clot formation usually
occurs in 3-6 minutes
• Within 1 hour of clot formation
– The clot begins to retract
– Pulls the damaged edges together
• Once the endothelium is regenerated, the clot
is broken down